Construction materials, such as gravel and the like, are often carried by trucks on public highways from their source of supply to the location where the materials will be utilized. Clearly, it is in the best interests of efficiency to carry the largest load of materials possible each trip to minimize the number of round trips necessary and thus minimize both labor and equipment costs. However, most jurisdictions have weight limits or bridge laws which restrict the gross vehicle weight as a function of the number of axles and the distance, or bridge, between certain of the axles. Further, in a vehicle having a dump body, i.e. a dump truck, a dump body that is excessively long can be inconvenient, and even dangerous to tip up in the dumping operation because of the instability of the truck as the body is tilted into the dumping position.
One satisfactory solution to these factors is the pull trailer dump truck system. The concept of this system apparently originated with Mr. J. R. Likens and is disclosed in his U.S. Pat. No. 2,849,129 issued on Aug. 26, 1958. In concept, the system employs a conventional dump truck with a tilting dump. The dump body can be tilted about a pivot axis at the rear of the truck into a dumping position to dump the material contained therein. The system also includes a trailer which is trailed behind the dump truck. The trailer includes a frame and a trailer body. The trailer body is mounted on rollers on the frame. Both the body on the dump truck and body on the trailer are filled with material, such as gravel, at the supply source. Because of the number of axles and the length of the dump truck and trailer, a heavy load of material can be carried legally under most bridge laws. For example, an 80,000 lb gross vehicle weight can be achieved with such a system, with the useful load carrying capacity of the assembly approaching 52,000 lbs.
When the assembly reaches the site where the material is required, the trailer is disconnected from the dump truck and the dump truck proceeds to dump its load in the conventional manner. When the dump body is empty, the dump truck is backed against the front of the trailer and the dump truck and trailer are locked together. A latching mechanism is operated to release the body on the trailer and a mechanism is activated to draw the body physically into the dump body on the dump truck where it is secured in place. The dump truck can then be disconnected from the trailer and driven off to dump the load within the trailer body now secured within the dump truck body.
After the trailer body is empty, the dump truck is again backed up and secured to the trailer and the trailer body moved back onto the trailer and secured in place by the latching mechanism. In effect, the combination allows two dump truck body loads to be carried in a single trip. The system has the further advantage of allowing a shorter dump body to be used on the dump truck than would be required to dump an equal amount of material if both loads were in a single dump body, thus reducing the instability of the dump truck when the dump body is moved into the dumping position.
The system, however, does have several disadvantages relating to the latching mechanism. The latching mechanism is a pivoting hook mounted on the trailer which is manually moved into a preliminary engagement position with a bar on the body, assuming the body is properly positioned on the trailer. A power cylinder, such as an air cylinder, then completes the latching by pivoting the hook down onto the bar. However, this latching mechanism requires a multiple step operation and that the body be properly positioned on the trailer. An operator could operate the latching mechanism with the trailer out of position, thinking that the body was properly latched to the trailer, when it is not. Therefore, a need exists for an improved system to provide more effective and secure locking of the body to the trailer.